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Types of loads
Load Rating and Life
Bearing Life
One of the most important factors when selecting bearings is the life of the bearing. Bearing life depends on the functions required of a machine.

Fatigue life … Life of the bearing in terms of material fatigue caused by rolling. Lubrication life … Life of the bearing in terms of burning caused by deterioration of lubricant.

Sound life … Life of the bearing in terms of obstruction of bearing function caused by increase of turning sound.

Wear life … Life of the bearing in terms of obstruction of bearing function caused by wear of the internal parts, single bore diameter and outside diameter of the bearing.

Precision life … Life of the bearing in terms of becoming unusable due to deterioration of the turning precision required by the machine.

In the case of fatigue life, the material becomes fatigued due to repeated load stress between the raceway and rolling elements, resulting in flaking. Duration of life can be predicted by statistical calculation. Generally speaking, fatigue life is treated as bearing life.
Basic Rating Life and Basic Dynamic Load Rating
When individual bearings of a group of the same type of bearing are turned under the same conditions, basic rating life is defined as the total number of times the bearing can be turned without flaking due to rolling fatigue in 90% (90% reliability) of the bearings.

Basic dynamic load rating expresses dynamic load capacity of rolling bearings, and therefore refers to a certain load, which provides basic rating life of one million revolutions. Basic dynamic load is expressed as pure radial load for radial bearings, and pure axial load for thrust bearings. Basic dynamic load rating Cr or Ca is given in the NTN catalog dimensions tables.
Basic rating life is calculated by equation 6.1 or 6.2.
L10 = ( C / P ) p ----------- (6.1)
L10h = 106 / 60n ( C/ P)p ----------- (6.2)

L10 : Basic rating life (106 revolutions)
L10h : Basic rating life h (hours)
C : Basic dynamic load rating N{kgf}
Cr : Radial bearing
Ca : Thrust bearing
P : Dynamic equivalent load N{kgf}
Pr : Radial bearing
Pa : Thrust bearing
n : Rotational speed rpm
p : Ball bearing p=3
Roller bearing p=10/3
In equipment with several bearings, if the life of one develops rolling fatigue, it is considered to be the total life for all the bearings. Life can be calculated by equation 6.3.
Life adjustment factor for operating condition a3 Coefficient for adjusting life for lubrication conditions, rotational speed, running temperature, and other operating conditions. If lubrication conditions are favorable, a3 is generally "1." If lubrication conditions are particularly good and other factors are normal, a3 > 1 may be used.

Oppositely a3 < 1 is used in the following cases:
1. If lubrication oil viscosity is low (13 mm2/s or less for ball bearing; 20 mm2/s for roller bearing)
2. Rotational speed is low (Rotational speed n by rolling element pitch circular dp, dp・n < 10,000)
3. If operating temperature is high (adjusted by Fig. 6.1 due to decrease in hardness)
Items that consider coefficient a2 by dimension stabilization treatment do not require adjustment of Fig. 6.1 as long as each is used within maximum operating temperature.

Bearings are affected by various conditions other than these, but are not clarified as the a3 coefficient. There is also the way of the a23 coefficient matching a2 and a3, but at the present there is need to overlap the data. In the case of an extremely large load, and there is danger of harmful plastic deformation developing on the contact surfaces of the rolling element and raceway, if Pr exceeds either Cor or 0.5 Pa in the case of radial bearings, or Pa exceeds 0.5 Ca in the case of thrust bearings, equations 6.1, 6.2 and 6.5 for calculating basic rating life cannot be applied.
Machine Applications and Requisite Life
6.4 Machine Applications and Requisite Life When selecting bearings, you must select bearings that provide the life required for the machine. The general standards for life are given
Basic Static Load Rating
Bearing load where contact stress of maximum rolling element load is the following values is defined as basic static load rating.

Ball bearing 4 200MP {428kgf/mm 2
Roller bearing 4 000MPa{408kgf/mm 2
These values are the equivalent of the load where permanent set of approximately 0.0001 time the rolling element diameter is produced by the load in the area where the rolling elements make contact with the raceway surface. It is empirically known that the degree of deformation is as far as smooth rotation of the shaft is not impeded. This basic static load rating is given in the dimension table as Cor and Coa for radial and thrust bearings respectively.
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